Why Surface Area Rather Than Weight
Body surface area correlates better with metabolic rate, cardiac output, blood volume and renal clearance than body weight does. This makes it the standard basis for dosing drugs with narrow therapeutic windows — chemotherapy above all — and for indexing cardiac measurements across body sizes.
The typical adult sits between 1.5 and 2.0 m², and 1.73 m² is the reference value used to normalise kidney function reporting.
The Formulas
| Formula | Year | Notes |
|---|---|---|
| Mosteller | 1987 | √(height × weight / 3600). Simplest, and the clinical default |
| Du Bois and Du Bois | 1916 | The original, derived from nine subjects; underestimates in obesity |
| Haycock | 1978 | Developed with paediatric data |
| Gehan and George | 1970 | Based on 401 direct measurements |
| Boyd | 1935 | Still specified in some oncology protocols |
They typically agree within 3–5%. Because chemotherapy doses scale directly with BSA, that difference is clinically meaningful, which is why protocols name the formula rather than leaving it to the prescriber.
Body Surface Area Chart
Mosteller values in m²:
| Height | 60 kg | 70 kg | 80 kg | 90 kg | 100 kg |
|---|---|---|---|---|---|
| 155 cm | 1.61 | 1.74 | 1.86 | 1.97 | 2.07 |
| 165 cm | 1.66 | 1.79 | 1.92 | 2.03 | 2.14 |
| 175 cm | 1.71 | 1.84 | 1.97 | 2.09 | 2.20 |
| 185 cm | 1.76 | 1.90 | 2.03 | 2.15 | 2.27 |
| 195 cm | 1.80 | 1.95 | 2.08 | 2.21 | 2.33 |
Where BSA Dosing Is Criticised
The practice dates from the 1950s and was based on limited evidence that it reduced inter-patient variability. Later analysis showed it explains only a small share of the variability in drug clearance for many agents. Obese patients are the clearest problem: BSA rises with weight, but drug clearance often does not, so unadjusted dosing risks toxicity. Many protocols now cap BSA at 2.0 m² or use adjusted body weight.
Other Uses
- Cardiac index — cardiac output divided by BSA, normally 2.5–4.0 L/min/m².
- Burn assessment — the rule of nines estimates the percentage of BSA affected, which drives fluid resuscitation.
- Renal function — eGFR is reported per 1.73 m².
- Paediatric dosing — where weight-based dosing does not scale reliably across a wide age range.
Frequently Asked Questions
Which formula should I use?
Mosteller, unless a protocol specifies otherwise. It is the simplest, agrees closely with the others, and is the most widely adopted.
Does BSA change with body composition?
The formulas use only height and weight, so two people with the same measurements and very different composition get the same BSA. This is a known limitation rather than an error.
What is a normal BSA?
Roughly 1.6–1.9 m² for adult women and 1.8–2.1 m² for adult men. Newborns are near 0.25 m².